1. Field of the Invention
The present invention relates to an electric linear actuator in which rotational movement of a motor, which is caused in response to input signals, is output after being converted into translational movement of a screw shaft by means of a feed screw mechanism, and more particularly, to an electric linear actuator having a clutch mechanism provided between a motor and a feed screw mechanism.
2. Description of the Related Art
Conventionally known examples of the electric linear actuator of this type include one disclosed in JP 2007-46637 A. The electric linear actuator transmits rotational movement of a motor to a nut member of a feed screw mechanism so that a screw shaft threadedly engaged with the nut member is caused to advance and retract in an axial direction in accordance with the rotation of the nut member.
While the motor is fixed to an actuator housing, the nut member is held by the actuator housing through an intermediation of a rotational bearing, and an output shaft of the motor and a rotation shaft of the nut member are provided parallel to each other. Multiple speed reduction gears transmit the rotation of the output shaft of the motor to the nut member, and when the motor is driven, the nut member is rotated in accordance with the rotational direction and the rotation amount thereof so that the screw shaft threadedly engaged with the nut member advances and retracts in the axial direction thereof.
Further, in the middle of the transmission path for the rotary power of the motor, which is constituted by the speed reduction gears, there is provided a clutch for controlling the rotational torque exchanged between the motor and the nut member. While transmitting rotational torque of the motor toward the nut member, the clutch prevents transmission of rotational torque toward the motor, the rotational torque being transmitted, when the nut member is rotated by an axial force acting on the screw shaft from the outside, from the nut member and received before being beared between the clutch and the actuator housing.
The electric linear actuator of this type is used, for example, in an electric reclining mechanism for airplane seats. In consideration of a use mode of the airplane seats, reclining positions have to be manually adjusted even when it becomes impossible to activate the motors thereof for some reasons or other. In this regard, in the above-mentioned conventional electric linear actuator, the clutch consequently bears the rotational torque generated by the nut member between the clutch and the actuator housing even when the screw shaft should be forcibly caused to advance and retract. Therefore, the screw shaft cannot be manually moved in the axial direction.
Further, each of the multiple speed reduction gears for transmitting the rotary power from the motor to the nut member is held by the rotational bearings. Thus, there has been a tendency that weight thereof is consequently increased owing to upsizing of the actuator housing in addition to the large number of components. In particular, weight reduction is highly demanded for the above-mentioned electric linear actuator used for airplane seats, and hence the number of components and downsizing thereof are highly demanded.